The long-term goal of this project is to develop novel endothelium-targeted therapies for the prevention and treatment of cardiovascular disease. Discovery of circulating endothelial progenitor cells (EPCs) revolutionized understanding of the mechanisms responsible for endothelial repair after vascular injury and revascularization of ischemic tissues. However, the mechanisms underlying beneficial effects of EPCs are poorly understood. Prostacyclin (PGI2) is one of the most important vasoprotective molecules released from vascular endothelium. Strikingly, the role of arachidonic acid metabolism and biosynthesis of PGI2 in regulation of regenerative function of EPCs has not been studied. In our preliminary studies we identified intrinsically high biosynthesis of PGI2 as one of the major phenotypic characteristics of human EPCs. Furthermore, our studies indicate that pharmacological or genetic inactivation of PGI2 significantly impairs regenerative capacity of EPCs. Therefore, the general hypothesis of this application is that in the cardiovascular system, biosynthesis of PGI2 in EPCs is an essential mechanism responsible for the regenerative function of EPCs. To test this hypothesis we propose studies with the following specific aims: 1) determine expression and function of cyclooxygenase (COX) isoforms and profile of prostanoids biosynthesis in human EPCs, 2) define the role of PGI2 in regenerative functions of EPCs, and 3) analyze the role of arachidonic acid metabolism in aging-induced decline in regenerative capacity of EPCs. Experiments will be performed on EPCs isolated from circulating blood of healthy young and aged volunteers. The role of EPCs-derived PGI2 in repair injured endothelium or angiogenesis will be studied in vitro and in vivo. Established models of wire-induced injury of common carotid artery and hind limb ischemia in nude mice will be employed to determine the role of PGI2 derived from EPCs in endothelial repair and revascularization. Genetic modification of human EPCs will be carried out to gain further mechanistic insight into the role of arachidonic acid metabolism in reparative functions and aging of EPCs. The proposed studies will provide currently missing information regarding the role of prostanoids released from EPCs in response of the cardiovascular system to injury and aging. Understanding of these mechanisms will establish basis for development of novel therapeutic approaches to prevention and treatment of cardiovascular diseases. PUBLIC HEALTH RELEVANCE: Project Narrative Endothelial Progenitor Cells (EPCs) are released from the bone marrow during cardiovascular diseases including myocardial infarction and stroke. Their major function is to repair injured blood vessels and restore normal cardiovascular function. Currently, efforts of many laboratories, including ours, are focused on understanding the mechanisms responsible for regenerative function of EPCs. The long-term goal of this application is to harness therapeutic potential of EPCs.